The findings of both clinical and experimental studies support the supposition that alterations in the flow of blood to and from the penis may be among the most frequent causes of organic impotence in humans. In fact, relaxation of the vascular smooth muscle in the penile corpora is now widely recognized as an obligatory step in penile rigidity, and may be impaired in a large proportion of impotent men. Thus, a better understanding of corporal vascular smooth muscle dysfunction is crucial to the development of therapeutic regimens that will effectively restore erectile potency. During the past two years we have used both steady-state and kinetic protocols to conduct detailed pharmacological analyses of isolated corporal tissue. In short, our studies have revealed that with advancing age, corporal vascular smooth muscle from impotent men is more efficiently contracted and less efficiently relaxed, by endogenously relevant receptor/effector systems. Given the complexity of hormonal regulation of corporal tome in vivo, an integrated approach is proposed that will combine studies at the intact tissue level with a cellular analysis of the cultured corpus cavernosum smooth muscle cells. The long- term goals of this grant proposal are to elucidate both intra- and intercellular mechanisms of signal transduction and response modulation in corpus cavernosal smooth muscle, and to identify potential alterations associated with erectile dysfunction. Specifically we shall: 1) Continue to use kinetic protocols to study the effects of age and disease on the interactions that occur when agonists activate receptor and/or effector systems that mediate functionally antagonistic responses in isolated intact corporal tissue strips; 2) Use novel steady-state protocols to examine the multiple receptor activation leading to mutual-effect amplification of contraction (i.e., synergism) in isolated intact corporal strips; 3) Evaluate the pharmacological and physiological importance of intercellular communication through gap junctions during contraction of isolated intact corporal strips; 4) Characterize the properties of the gap junctions in explanted corporal vascular smooth muscle cells using molecular biological, immunocytochemical and electrophysiological techniques; 5) Use calcium imaging techniques for real-time analysis of intracellular calcium homeostasis and regulation in cultured corporal vascular smooth muscle cells, as well as the role of gap junction channels in the propagation of calcium waves between cells. The emphasis in this proposal on kinetic and steady-state studies of both single and multiple receptor activation (on intact tissues as well as cells), should provide important new information about signal transduction and response modulation in vascular smooth muscle, and may more closely approximate events likely to occur in vivo.